Whether this VA is a man sounding like a woman or a woman trying to sound like a man, the basic tone of the voice IS the same. However, as we experienced with Ed as well, chances are that the actors don't get much of a chance to get to know their characters before they begin to play them. Soon Envy will have to have malice and sadisticness, and the VA will realize..."hey, this is how I have to sound to pull this off."
Let's not write off Envy's VA so quickly. It's not like Gluttony, where his entire character is changed by the voice. They are still fundamentally very close.
Al, when your brother is about to die, usually you raise your voice a little bit.